Hackers have stolen the email addresses of some of TripAdvisor.com’s 20 million members.

Travel site TripAdvisor sent out an email to its registered users today, announcing that the site had been hacked, and some member emails had been “stolen” by an “unauthorized third party.” The company says no email passwords were taken by the hackers.

“We’ve confirmed the source of the vulnerability and shut it down,” says TripAdvisor co-founder and CEO Steve Kaufer. “We’re taking this incident very seriously and are actively pursuing the matter with law enforcement.”